The invention relates to an accurate pressure gauge with a simple structure which is easy to manufacture and assemble.
In order for convenience and practicality in use, watch-like pressure gauges are the most common. Referring to FIGS. 1 and 2A through 2C, a common watch-like pressure gauge icludes a housing 1, including a tube portion 101 longitudinally formed on the upper end thereof and having an inward flange 1011 at the lower end of the tube portion 101, a right support rod A fixed on the right of the housing 1 and including a first tongue at the end thereof, a left support rod B fixed on the left of the housing 1 and including a second tongue at the end therof, a bearing 102 fixed on the center of the housing 1, and a pivot pin 103 fixed on the housing below the left support rod B; a tube member 2, connected insertably to the upper end of the tube portion 101, including a flexible upper end portion with an air inlet 201; a seal member 3 of rubber material, movably disposed in the tube member 2 near the air inlet 201; a push rod 4, disposed in the space defined collectively by the tube portion 101 and the tube member 2, extending outwardly of the tube portion 101 at the lower end of the push rod 4, having an outward flange 41 at the upper end of the push rod 4 for abutting on the under surface of the seal member 3; a compression spring 5 disposed in the tube portion 101 and the tube member 2 for biasing the seal member 3 against the pressure exerted on the seal member 3; a sector member 6, pivotally mounted on the right support rod A, including an upper radius, a lower radius, a toothed arc 61 engaging with the pinion member 81, and a blocking plate 62 projecting from the lower radius for blocking the lower end of the push rod 4; a first torsion spring 7, pivotally mounted on the right support rod A for biasing the sector member 6 to rotate anticlockwise; an axle 8, journalled on the bearing 102, including a pinion member 81 fixedly mounted on the axle 8; a support sheet C having two circular holes at the opposite ends thereof for sleeving on the tongues of the support rods A and B, and a first central hole for having inserted therethrough the axle 8; an indicating needle 9, secured to the end of the axle 8; an indicating board 10, having a second central hole for having inserted therethrough the axle 8 to be located between the support sheet C and the indicating needle 10, and a blocking rod 1001 mounted on the indicating board 9 at an end of the indicating mark for preventing the indicating needle 9 from undesired directional rotation; a second torsion spring 11, pivotally mounted on the pivot pin 103 and extending around a portion of the axle 8 for gripping the axle 8 to prevent the axle from rotation; and a push button 12, fixed on the housing 1 and connectd to the free end of the second torsion spring 11 for pushing thefree end of the second torsion spring 11 to release the second torsion sprig 11 from the axle 8. The gripping force of the second torsion spring 11 against the axle 8 is larger than the bias force of the first torsion spring 7 against the sector member 6.
In use, referring to FIG. 2A, when the air inlet 201 initiates communication with the inside of an article, such as a tire, the seal member 3 will be exerted by the air pressure inside of the article to push the push rod 4 downwardly, thereby pushing the blocking plate 62 and hence the sector member 6 to rotate anticlockwise. By the engagement of the toothed arc 61 and the pinion member 81, the axle 8 is driven to rotate clockwise so that the indicating needle 9 indicates the value of the air pressure. After the article disengages from the air inlet 201, referring to FIG. 2B, the tension spring 5 will bias the push rod 4 and hence the seal member 3 to restore the original position. On the other hand, due to the gripping of the second torsion spring 11 against the axle 8, the first torsion spring 7 fails to bias the sector member 6 to move up so that the indicating needle 9 remains fixed. This enables the pressure gauge to be held conveniently before the eyes of the user. Subsequently, when the value of the pressure is known, the push button 12 is actuated to release the axle 8 from being gripped by the second torsion spring 11 so as to permit the first torsion spring 7 to bias the sector member 6 to move up, thereby permitting the indicating needle 9 to be restored to the initial position.
In the conventional pressure gauge, every tooth of the arc of the sector member 6 is very small, so relatively high accuracy is necessary during manufacture. Additionally, dust on the small teeth of the arc easily causes undesired errors in measurement.